A ring of Myrkul was a relatively thick gold band painted black adorned with an image of a white flaming skull (the symbol of Myrkul).
Evil, intelligent creatures who passed within 30 feet of a ring of Myrkul were drawn to it.
Rings of Myrkul served as keys for priests of Myrkul to enter a temple of Myrkul safely. They also allowed the wearer the ability to walk among the undead without being attacked (unless the wearer attacked the undead). Additionally, the rings had a few offensive abilities, including casting the spells chill touch and ghoul touch.
During an astronomical event, known as "the Eye of Myrkul", when a new moon passed through a ring of stars associated with the symbol of Mystra, the rings of Myrkul manifested the power to raise the Uthtower from the swamps of the Mere of Dead Men. Three such rings were required to be within five miles of the tower to raise it, and the rings were able to magically guide a wearer toward the tower if so desired.
While within the Uthtower, a ring's other powers to affect the undead and cast necromantic spells were also enhanced.
When Myrkul was killed in 1358 DR, his secret temple in the Mere of Dead Men in the Sword Coast North sank into the swamp. The priests escaped into the Mere but were killed, their rings falling into the possession of the beasts of the Mere.